1. Field of the Invention
The present disclosure relates to an organic light emitting diode display device. The present disclosure also relates to an active matrix organic light emitting diode display device and a method of fabricating the same.
2. Discussion of the Related Art
As the information society progresses, importance of a flat panel display (FPD) has increased. Although a liquid crystal display (LCD) device has been overwhelming in market share among various FPDs, an organic light emitting diode (OLED) display device is getting the spotlight as a next generation FPD due to a light weight, a thin profile and a low power consumption as compared with the LCD device having an additional light source, a color shift according to a viewing angle and a high power consumption. The OLED display device having excellent viewing angle and contrast ratio is easily applicable to a flexible substrate and has an emissive type where an additional light source is not necessary. As a result, the OLED display device is more easily applicable to a next generation FPD such as a flexible display and a transparent display as compared with the LCD device.
The transparent display requires a transmittance of about 35% to about 40% for users to watch an image of the OLED panel and a background behind the OLED panel. However, since an area for driving elements such as thin film transistors for driving a light emitting diode is relatively wide, the OLED display device has a limit in increasing the transmittance.
FIG. 1 is a plan view showing a transparent organic light emitting diode display device according to the related art, and FIG. 2 is a cross-sectional view taken along a line II-II of FIG. 1.
In FIGS. 1 and 2, a transparent organic light emitting diode (OLED) display device according to the related art includes a pixel region PX defined by a gate line GL, a data line DL and a power line VL. The pixel region PX includes an emitting area EA and a transparent area TA, and driving elements 130 are formed in the emitting area EA. The transparent area TA may be transparent or substantially transparent for visible light. The presence of the driving elements 130 in the emitting area EA may have the effect that the emitting area EA has a lower transmittance for visible light compared to the transparent area TA. For example, the emitting area EA may be substantially non-transparent for visible light. Among the driving elements in the emitting area EA, a storage capacitor has the largest area. The storage capacitor includes first and second capacitor electrodes 110 and 120 facing and spaced apart from each other. The capacitance of the storage capacitor is proportional to an area of the first and second capacitor electrodes 110 and 120 and is inversely proportional to a gap distance between the first and second capacitor electrodes 110 and 120. Accordingly, as the area of the first and second capacitor electrodes 110 and 120 increases and as the gap distance between the first and second capacitor electrodes 110 decreases, the capacitance of the storage capacitor increases.
The storage capacitor keeps the emission of the light emitting diode during a frame. As a result, a sufficient capacitance of the storage capacitor is required to keep the emission during a frame. However, when the area of the first and second capacitor electrodes 110 and 120 is enlarged for a sufficient capacitance, an area of the transparent area TA is reduced and it is difficult to obtain the transmittance of about 35% to about 40%.
In addition, since only a pair of storage electrodes 110 and 120 are formed, there is a limit to increase of the capacitance. In a bottom emission type OLED display device, when the first and second capacitor electrodes 110 and 120 are enlarged, the area for the driving elements increases and the area for the emitting area EA decreases, thereby the emission efficiency is reduced. Further, since the higher power consumption is required to obtain the sufficient emission efficiency, the lifetime of the light emitting diode is shortened. In a top emission type OLED display device, although increase in the area of the first and second capacitor electrodes 110 and 120 does not directly affect the area of the emitting area EA, there is a limit to obtain high resolution.